This invention relates to electromagnet heads and, more particularly, to a head in which the addressability resolution function and the imaging resolution function are separated, permitting construction with differing degrees of precision of large pedestals for addressability resolution and respectively related small pedestals for imaging resolution.
Magnetographic printing systems employ a print head, a magnetizable medium, and a toner for producing an image on a sheet of paper or other hard copy material. The magnetic medium may be carried upon a drum or upon a tape. Typically, the magnetic medium is coated upon the drum or the tape. The print head comprises an array of magnet cores which are interlaced with a set of electric conductors. The magnetic cores, in cooperation with the electrical conductors, form electromagnets which are selectively energizable by application of electric currents to selected ones of the electric conductors.
The print head is positioned alongside of the surface of the magnetic medium to allow each of the electromagnets to impart a magnetic field to the medium in a region directly beneath the terminus, or print-element portion, of a magnetic core, thereby to write a mark upon the magnetic medium. Energization of various ones of the electromagnets results in the formation of a set of marks on the magnetic medium, which set of marks constitute an image written on the medium by the print head. The magnetic image is rendered visible by toning with magnetic ink, which ink is attracted by the local magnetic fields of the magnetically written regions. The toner is then transferred to the paper to produce the image on the paper.
In many printing applications, it is desirable to produce a high-resolution image. By way of example, such high-resolution imaging is required in the printing of small detailed characters, such as a 9-point text. A further example is the case of the printing of a picture wherein fine detail is to be rendered. In order to accomplish fine-resolution printing rapidly, it is desirable to construct a print head having an array of many closely spaced small print elements, the size of the print elements being commensurate with the smallest detail to be rendered.
A problem arises in the construction of a print head of closely-spaced high-resolution print elements. The problem is that toner is most strongly attracted to the periphery of the imaged region on the image receptor, leaving the center lightly toned. A gross example is the grey area which appears in the middle of a large black area in a photocopy. When two pel images overlap, the toner adheres only to the periphery of the double image, leaving a double center untoned. It therefore is extremely advantageous for pel spots to be placed closely but not to overlap. Heretofore, both the print elements and their corresponding electrical activation conductors had to be constructed using expensive high-resolution processing technology, and since the conductors have to be electrically continuous over relatively long distances, this high-resolution processing had to be done over a large area. These considerations have made large, page-wide, high-resolution print heads expensive to produce.